A particularly thorny area of evaluation is the impact of transportation investment on induced travel and development…While many researchers believe that these [induced travel] impacts exist, it is extremely difficult to demonstrate their presence even for aggregate investments and certainly for a specific project. For this first round, we take the conservative position that these impacts are not sufficiently quantifiable for measurement at the provincial level. [Emphasis added.]

Expert opinion is perfectly clear on this issue: induced travel (the “If you build it, they will come” effect) is a real and widely observed phenomenon. When you construct new or wider roads in an urban area, people will find reasons to drive on them. In some ways it’s an effect that transportation planners are counting on: if people didn’t use the new roads, the money spent to build them would have been wasted, right? The question, then, isn’t whether new or wider roads get filled; it’s how quickly.

Todd Litman has reviewed the relevant literature on induced travel and generated traffic, and finds that new traffic can fill 50 to 100 percent of new urban road space within 3 years after a new road is opened. So any responsible evaluation of road construction ought to consider induced travel—at least nominally, and with rough estimates where precise ones are impossible.

But the Fraser Institute prefers another tack: since generated traffic is hard to estimate in advance, they’ve decided to ignore it entirely. This suits their purposes quite nicely, since as Todd shows, much of their evaluation is geared towards showing how lovely roads are. The fact that new roads can get clogged quite quickly with new traffic doesn’t fit the roads-are-beautiful leitmotif.

In case you’re wondering, the Fraser Institute positions itself as a “conservative” research center; and this paper claims that it takes a “conservative” approach to the question of induced traffic. But apparently, “conservative” in this case means “ignoring reality” and “wildly underestimating.” That sort of approach doesn’t seem particularly “conservative” to me—and if they’re trying to present themselves as a credible research center with smart ideas, they’ve done yourself a disservice with on this bit.

Todd has a longer critique of the Fraser Institute report here (pdf link), if you’re interested.

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Comments

Eric de Place says:

November 6, 2008 at 4:55 pm

I don’t know Clark… As an innately lazy person I kind of like the idea that if something is complicated and hard to quantify then it must not have a serious impacts and is therefore not worth bothering about. By that reasoning we can all start ignoring climate change, the business cycle, and epidemiology—just to name a very few topics. I’m going to enjoy this new simpler world!

Obviously, you did not read the study to ascertain the definition of induced travel that is used. In the literature, induced travel has many meanings: some include growth in VMT; some include shifting of VMT from one part of the network to the new additions; and some include new travel, made only because the travel is possible because of the new additions. (Personnlay, I think true induced travel is only the last category.) This study included the growth in VMT and shifts in VMT, but not the new VMT, which is hard to project and quantify. Of course, most of the fill on new highways comes from latent demand. If we kept up with highway construction, then we would not have such rapid fill-ups of our new roads. Just as if we kept up with school construction, we would not fill up schools within 3 years of opening. The “if you build it, they will come” mentality is highly simplistic and clearly not always true. Buffalo, NY has plenty of roads, but traffic is declining as people flee that region of the US. It’s foolish to think that if Buffalo offcials built new roads, people would flock there to fill them up. It’s funny how people are selective in their terminology: if light rail supporters build a rail line and it’s used extensively, they never say, “Look at the travel we’ve induced.” Insted they say, “See how we are meeting the needs of the people!”